TWI896845B - Polarizing plate and manufacturing method thereof - Google Patents

Abstract

The present invention aims to provide a novel polarizing plate that suppresses the poor appearance caused by thermal shrinkage of polarizing film and exhibits excellent durability. The present invention addresses this problem by providing a polarizing plate comprising: a polarizing film made of a polyvinyl alcohol-based resin; and a light-transmitting support substrate laminated on at least one side of the polarizing film via a bonding layer. The bonding layer is formed from a molecular bonding agent that chemically bonds the polarizing film to the support substrate.

Description

Polarizing plate and manufacturing method thereof

The present invention relates to a polarizing plate, and more specifically, to a polarizing plate formed by laminating a polarizing film made of a polyvinyl alcohol-based resin and a light-transmitting supporting substrate through a molecular binder.

Conventionally, as an optical component that allows light polarized in a specific direction or wavelength to pass through, a polarizing plate is known. It consists of a polarizing film made of a polyvinyl alcohol-based resin (PVA polarizing film) laminated onto a light-transmitting support substrate such as glass or crystal via an adhesive.

[Prior Art Literature] [Patent Literature]

[Patent Document 1] WO13/154139

The PVA film used in polarizing plates is made by adsorbing iodine or a dichroic dye onto a uniaxially stretched polyvinyl alcohol-based resin film. However, due to its characteristic absorption of light parallel to its absorption axis, PVA film can experience thermal shrinkage due to the absorbed light energy, causing the film's temperature to rise, generating shrinkage stress in the stretching direction. This shrinkage can cause cosmetic deformation (or unsightly appearance) such as unevenness or wrinkles. In display devices such as liquid crystal displays, this unsightly PVA film can result in poor image quality or reduced contrast.

On the other hand, high brightness and precision are required in image display devices. In recent years, light sources with large or high values such as beam size, luminosity, brightness, and optical density have been used. When using such light sources, the amount of light energy absorbed by the PVA polarizing film increases, making the appearance defects caused by thermal shrinkage of the PVA polarizing film more noticeable.

The present invention was developed in response to this problem. Its purpose is to provide a novel polarizing plate that suppresses the appearance defects caused by thermal shrinkage of PVA polarizing film and exhibits excellent durability.

The inventors of this invention have diligently researched ways to suppress the appearance defects caused by thermal shrinkage of the polarizing film in polarizing plates. They discovered that by using molecular bonding technology to chemically bond the PVA polarizing film to the supporting substrate, the PVA polarizing film and the supporting substrate can be more firmly bonded. This technology also effectively dissipates heat generated by the PVA polarizing film to the supporting substrate, reducing the thermal load on the PVA polarizing film. This led to the completion of the present invention.

According to the present invention, a polarizing plate is provided, characterized by comprising: a polarizing film made of a polyvinyl alcohol-based resin; and a light-transmitting support substrate laminated on at least one side of the polarizing film via a bonding layer. The bonding layer is formed from a molecular bonding agent that chemically links the polarizing film to the support substrate.

Furthermore, the present invention provides a method for manufacturing a polarizing plate, comprising: providing a molecular binder on the surface of a polarizing film made of a polyvinyl alcohol-based resin and/or a light-transmitting support substrate; layering the polarizing film and/or the support substrate via the molecular binder present on the surface; and bonding the polarizing film and the support substrate by heat pressing to chemically bond the polarizing film and the support substrate.

The polarizing plate of the present invention utilizes chemical bonding to bond the PVA polarizing film to the supporting substrate, thereby reducing the thermal load on the PVA polarizing film and suppressing any cosmetic defects caused by thermal shrinkage of the PVA polarizing film. Furthermore, the polarizing plate of the present invention utilizes chemical bonding to bond the PVA polarizing film to the supporting substrate, ensuring strong adhesion between the supporting substrate and the polarizing film, thereby suppressing any cosmetic defects caused by thermal shrinkage of the PVA polarizing film.

1:Polarizing plate

2:Polarizing film

3: Joint layer

4: Support substrate

[Figure 1] is a cross-sectional view showing an example of the polarizing plate of the present invention.

The present invention is described in detail below. Furthermore, the present invention is not limited to the following forms and can be configured in various forms within the scope of achieving the effects of the present invention.

[Polarizing plate]

FIG1 shows an example of a polarizing plate of the present invention. The polarizing plate 1 shown in FIG1 comprises: a polarizing film 2 made of a polyvinyl alcohol-based resin; and a supporting substrate 4 laminated on at least one side of the polarizing film 2 via a bonding layer 3. More specifically, the polarizing film 2 is laminated via a bonding layer 3 formed by a molecular bonding agent using a molecular bonding technology that chemically bonds the polarizing film 2 to the supporting substrate 4. Molecular bonding technology is a technology that chemically bonds components using one to several layers of molecules. Polarizing plates bonded using molecular bonding technology have higher thermal conductivity than conventional bonding methods using intermolecular forces, which can reduce the thermal load of the polarizing film and thus suppress poor appearance caused by thermal shrinkage of the polarizing film. Furthermore, polarizing plates bonded using molecular bonding technology are directly joined by chemical bonding, resulting in higher adhesion compared to conventional bonding methods based on intermolecular forces. Furthermore, since the polarizing film and the supporting substrate are firmly bonded, thermal shrinkage of the polarizing film and any resulting cosmetic defects can be suppressed. Therefore, polarizing plates bonded using molecular bonding technology possess high durability, maintaining the performance of the polarizing film over a long period of time. Furthermore, although not shown, another supporting substrate can be placed on the other side of the polarizing film, interposed through a bonding layer formed by a molecular bonding agent.

[Polarizing film]

Polarizing films are made of polyvinyl alcohol-based resin films that exhibit absorption dichroism at wavelengths between 380 and 780 nm. Examples of polarizing films exhibiting absorption dichroism at wavelengths between 380 and 780 nm include polyvinyl alcohol-based resin films with iodine and/or dichroic dyes adsorbed and aligned (H-type polarizing films) and polyvinyl alcohol-based resin films with light-absorbing stretched vinyl blocks formed in the polymer by dehydration (K-type polarizing films).

An H-type polarizing film formed from a polyvinyl alcohol-based resin adsorbed and aligned with iodine and/or a dichroic dye can be produced, for example, by the following method, which includes: uniaxially stretching the polyvinyl alcohol-based resin film; dyeing the polyvinyl alcohol-based resin film with iodine and/or a dichroic dye and allowing the dye to adsorb onto the film; crosslinking the polyvinyl alcohol-based resin film adsorbed with iodine and/or a dichroic dye using a crosslinking solution such as an aqueous boric acid solution; and washing the polyvinyl alcohol-based resin film with water.

As the polyvinyl alcohol-based resin, a saponified polyvinyl acetate-based resin can be used. Polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other copolymerizable monomers. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, alkenes, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides containing ammonium groups.

The saponification degree of polyvinyl alcohol resins is typically 85-100 mol%, preferably 98 mol% or higher. Polyvinyl alcohol resins may be modified; for example, aldehyde-modified polyvinyl formal or polyvinyl acetal may be used. The average degree of polymerization of polyvinyl alcohol resins is typically 1,000-10,000, preferably 1,500-5,000. The average degree of polymerization of polyvinyl alcohol resins can be determined according to JIS K 6726.

Films made from this polyvinyl alcohol-based resin can be used as a base film for polarizing films. The method for forming the polyvinyl alcohol-based resin into a film is not particularly limited, and known methods can be employed. The thickness of the polyvinyl alcohol-based base film is not particularly limited, but is preferably 10 to 200 μm, for example.

Uniaxial stretching of polyvinyl alcohol-based resin films can be performed before, simultaneously with, or after dyeing with iodine and/or dichroic dyes. If uniaxial stretching is performed after dyeing, it can be performed before or during crosslinking. Alternatively, uniaxial stretching can be performed in multiple stages. Uniaxial stretching can be performed between rolls with different circumferential speeds or using heated rolls. Uniaxial stretching can be performed dry in the open air or wet while the polyvinyl alcohol-based resin film is swollen using a solvent or water. The stretching ratio is typically 3 to 8 times.

To dye a polyvinyl alcohol-based resin film with iodine and/or a dichroic dye, for example, the film can be immersed in an aqueous solution containing iodine and/or a dichroic dye. Furthermore, the polyvinyl alcohol-based resin film is preferably immersed in water before the dyeing treatment.

An example of a post-dye crosslinking treatment is immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing boric acid. The crosslinking treatment can be performed in a single step or in multiple steps.

The post-crosslinking washing treatment can be performed, for example, by immersing the dyed, cross-linked polyvinyl alcohol-based resin film in water; spraying the film with water; or combining immersion and spraying. Following the washing treatment, the polyvinyl alcohol-based resin film can be dried using known methods.

A K-type polarizing film made from a polyvinyl alcohol resin containing light-absorbing stretched vinyl blocks by dehydrating the polyvinyl alcohol resin can be produced, for example, by the following method, comprising: uniaxially stretching the polyvinyl alcohol resin film; dehydrating the polyvinyl alcohol resin film; crosslinking the dehydrated polyvinyl alcohol resin film with a crosslinking solution such as an aqueous boric acid solution; and washing the polyvinyl alcohol resin film. The base film is the same as described above.

The uniaxial stretching of polyvinyl alcohol-based resin films can be performed at various stages. For example, uniaxial stretching can be performed before dehydration, simultaneously with dehydration, or simultaneously with or before or after boric acid crosslinking after dehydration. Furthermore, uniaxial stretching can be performed at multiple stages. The uniaxial stretching method is the same as described above.

A polyvinyl alcohol resin film can be dehydrated, for example, by exposing it to an acid with a pH of 3 or higher, followed by heating the exposed film. Specifically, the film can be immersed in deionized water for approximately 1 second to approximately 5 minutes, followed by immersion in an acid with a pH of 3 or higher for the desired period of time. Alternatively, the film can be exposed to the dehydrating catalyst using various methods. For example, the film can be immersed or soaked in an aqueous dehydrating catalyst for a sufficient dwell time to allow the catalyst to diffuse into the film.

The acid used in the dehydration treatment can be any acid that has a pH of 3 or higher and can remove hydrogen atoms and oxygen atoms from the hydroxylated portions of the linear polymer under heat or other appropriate treatment conditions, leaving conjugated ethylene units. Specific examples include hydrochloric acid, hydrobromic acid, hydroiodic acid, phosphoric acid, and sulfuric acid. Furthermore, these acids may be diluted with water or an alcohol such as methanol.

After exposing a polyvinyl alcohol-based resin film to a dehydration catalyst, the polyvinyl alcohol-based resin film and the adsorption catalyst can be heated to convert a portion of the alignment film into polyvinylene, the desired dehydration product. The film can be heated by conduction heating, convection heating, radiation heating, or a combination thereof. For example, the film and catalyst can be passed through a heated oven at a temperature ranging from approximately 88°C to approximately 205°C for a period of approximately several seconds to approximately 10 minutes. Alternatively, the film and catalyst can be exposed to microwave radiation, laser heating, or infrared radiation heating.

During the dehydration step, a portion of the vinyl alcohol polymer in the polyvinyl alcohol resin film is converted into polarizing molecules in a block copolymer of poly(ethylene ethylene-co-vinyl alcohol). The dehydration treatment results in the formation of conjugated poly(ethylene ethylene) blocks from the polyvinyl alcohol blocks. By aligning the PVA matrix in one direction, the transition moment of the conjugated poly(ethylene ethylene) blocks is also aligned, resulting in a material with pronounced dichroism.

An example of a post-dehydration crosslinking treatment is immersing the dehydrated polyvinyl alcohol resin film in an aqueous solution containing boric acid. Specifically, the dehydrated polyvinyl alcohol resin film can be exposed to a 10-20% boric acid aqueous solution at a temperature of 85-95°C.

The post-crosslinking water washing treatment can be performed, for example, by immersing the dehydrated, cross-linked polyvinyl alcohol-based resin film in water; spraying it with water; or combining immersion and spraying. Furthermore, after the water washing treatment, the polyvinyl alcohol-based resin film can be dried using known methods.

The thickness of the polarizing film is not particularly limited, but is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less. The thickness of the polarizing film is generally 1 μm or greater, preferably 3 μm or greater.

[Joint layer]

The bonding layer is made of a molecular bonding agent that uses molecular bonding technology to chemically bond the polarizing film to the supporting substrate. Molecular bonding technology involves chemically bonding components using one to several layers of molecules. For example, the surface of the adherend is converted into a surface with a single type of functional group, and bonding is achieved through bonding of these functional groups.

The molecular bonding agent preferably comprises a triazine derivative having a functional group that chemically bonds the polarizing film to the supporting substrate. The bonding layer formed from the molecular bonding agent comprising the triazine derivative preferably comprises the triazine derivative as a main component. Here, "main component" means a component comprising 50% by weight or more of the components of the bonding layer, preferably 60% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more.

The triazine derivative is preferably a compound containing two or more OH groups and/or OH-generating groups and one triazine ring. Triazine derivatives containing two or more OH groups and/or OH-generating groups and one triazine ring form a chemically bonded bonding layer through dehydration condensation between OH groups on the support substrate surface and/or OH groups on the polarizing film surface and the OH groups or OH-generating groups of the triazine derivative. Conventionally known triazine derivatives can be used. The OH group or OH-generating group is preferably an alkoxysilyl group.

The molecular binder may contain ingredients other than triazine derivatives, as long as they do not hinder the effects of the present invention. Examples of ingredients other than triazine derivatives include crosslinking agents, fine particles, UV absorbers, defoaming agents, thickeners, dispersants, surfactants, catalysts, lubricants, and antistatic agents.

The thickness of the bonding layer is not particularly limited. For example, it is preferably 5 μm or less and 0.001 μm or more, more preferably 1 μm or less and 0.001 μm or more, even more preferably 0.1 μm or less and 0.005 μm or more, and particularly preferably 0.05 μm or less and 0.01 μm or more. A thinner bonding layer thickness is preferred to efficiently dissipate heat generated by the polarizing film and suppress temperature increases in the polarizing film. However, if the surface properties of the adherend are poor, the OH groups of the triazine derivative on the surface of the polarizing film and/or the supporting substrate, or OH groups generated from OH-generating groups, may have difficulty contacting the other surface. Therefore, appropriate design should be considered to ensure this.

Furthermore, while dehydration condensation can occur between the OH groups on the substrate surface and the OH groups on the polarizing film surface, the surface roughness of both surfaces limits the contact area, resulting in extremely low adhesion. A bonding layer thickness of 0.05μm or less and 0.01μm or greater compensates for the surface roughness of the substrate and polarizing film, increasing the contact area and improving bonding strength.

[Supporting substrate]

The support substrate supports the polarizing film, which is easily broken and difficult to handle as a single unit, making it easier to handle and protecting it. It is made of a material that is translucent to visible light. Transparency here refers to a total light transmittance of 80% or higher, preferably 85% or higher, and even more preferably 90% or higher. Light transmittance can be measured in accordance with JIS K 0115 using a spectrophotometer (UV-Visible Near-Infrared Spectrophotometer "V-570" manufactured by JASCO Corporation).

Examples of materials that are translucent to visible light include organic materials, inorganic materials, and organic-inorganic hybrid materials. Examples of organic materials include triacetyl cellulose, diacetyl cellulose, polyester resins, polyimide resins, polyamides, polyolefin resins such as polyethylene and polypropylene, cycloolefin resins such as cycloolefin polymers and cycloolefin copolymers, polyether sulfones, polysulfones, polyvinyl chloride, acrylic resins, polycarbonate resins, and urethane resins. Examples of inorganic materials include silicate glass, borosilicate glass, titania silicate glass, fluoride glasses such as zirconium fluoride, fused silica, crystal, sapphire, YAG crystal, fluorite, magnesium oxide, and spinel ( _MgO - _Al2O3 ). Examples of organic-inorganic hybrid materials include resins made from silsesquioxane derivatives containing organic functional groups such as (meth)acrylic groups.

To efficiently dissipate heat generated by the polarizing film and suppress thermal contraction, the support substrate laminated on at least one side of the polarizing film preferably has a higher thermal conductivity than the polarizing film. For example, the thermal conductivity is preferably 0.7 W/mK or higher, more preferably 1 W/mK or higher, and even more preferably 5 W/mK or higher. Examples of such materials include sapphire (thermal conductivity: 40 W/mK) and crystal (thermal conductivity: 8 W/mK).

The thickness of the support substrate is not particularly limited and can be appropriately designed as long as it facilitates handling of the polarizing film and protects the polarizing film. For example, it is 10-3000μm, preferably 20-1500μm, and more preferably 30-1000μm.

Various functional layers can be formed on the surface of the support substrate as needed. Examples of these functional layers include conductive layers, antistatic layers, non-glare layers, antifouling layers such as photosensitive media layers, antireflective layers, hard coatings, UV shielding layers, heat shielding layers, electromagnetic wave shielding layers, and gas barrier layers.

[Polarizing Plate Manufacturing Method]

Next, the polarizing plate manufacturing method is explained. The polarizing plate manufacturing method comprises: providing a molecular binder on the surface of a polarizing film made of a polyvinyl alcohol-based resin and/or a light-transmitting support substrate; layering the polarizing film and/or support substrate through the molecular binder present on their surfaces; and heat-pressing the polarizing film and support substrate to bond them together by chemical bonding.

<Step 1: Preparation>

First, prepare the aforementioned polarizing film and support substrate. The polarizing film and support substrate can be in the form of a strip or sheet. The surface of the polarizing film and support substrate can be cleaned as needed, for example, by cleaning with a cleaning agent such as ethanol or acetone. The surface of the polarizing film and support substrate can also be activated by treatments such as UV irradiation, coma discharge treatment, or plasma treatment.

Furthermore, a solution or dispersion containing the molecular binder is prepared. The molecular binder can be diluted with a solvent. Examples of the solvent include water, alcohols (e.g., methanol, ethanol, isopropyl alcohol, ethylene glycol, propylene glycol, celite, carbitol), ketones (e.g., acetone, methyl ethyl ketone, cyclohexanone), aromatic hydrocarbons (e.g., benzene, toluene, xylene), aliphatic hydrocarbons (e.g., hexane, octane, decane, dodecane, octadecane), esters (e.g., ethyl acetate, methyl propionate, methyl phthalate), ethers (e.g., tetrahydrofuran, ethyl butyl ether, anisole), and mixtures thereof. The content of the triazine derivative can be appropriately set based on the coating process, for example, 0.0001-10 wt%, preferably 0.001-3 wt%, and more preferably 0.01-2 wt%.

<Step 2: Painting>

A molecular binder is applied to the surface of the polarizing film and/or supporting substrate. Specifically, this is achieved by applying a solution containing the molecular binder to the surface of the polarizing film and/or supporting substrate. Drying is then performed as necessary to allow the solvent to evaporate, leaving the molecular binder residue on the surface of the polarizing film and/or supporting substrate. The coating method is not particularly limited, and known methods can be employed, such as wire bar coating, immersion coating, spraying, rotary coating, roll coating, gravure coating, air knife coating, curtain coating, inclined plate coating, extrusion coating, and die coating. The drying method is not particularly limited, and a known method can be used.

<Step 3: Layering>

After a molecular binder is applied to the surface of the polarizing film and/or supporting substrate, the polarizing film and/or supporting substrate are layered through the molecular binder present on the surface of the polarizing film and/or supporting substrate. Specifically, this is achieved by layering the polarizing film and/or supporting substrate so that the surfaces coated with a solution containing the molecular binder are facing each other.

<Step 4: Heat Pressing>

Next, the polarizing film and the support substrate are heat-pressed, chemically bonding them together. Specifically, this is achieved by applying pressure while heating with the polarizing film facing the support substrate; applying pressure while heating with the support substrate facing the side of the polarizing film; or applying pressure from both the polarizing film and the support substrate.

The pressing pressure is sufficient to cause the OH groups of the triazine derivatives, or OH groups generated from the OH-generating groups, present on the surface of the polarizing film and/or the supporting substrate to contact the other surface. The pressing pressure is preferably, for example, 0.01 to 50 MPa, more preferably 0.1 to 20 MPa, even more preferably 0.5 to 10 MPa, and particularly preferably 0.5 to 5 MPa. The application time is, for example, 0.1 to 200 minutes. Consequently, even if the surface of the polarizing film or the supporting substrate has minute irregularities, the polarizing film or the supporting substrate will deform accordingly, allowing the OH groups of the triazine derivatives present on these surfaces to reach the other surface and bond. In other words, the polarizing film and the supporting substrate are firmly bonded through chemical bonding (reaction) of the triazine derivatives. The heating temperature is a temperature that promotes the chemical reaction of the triazine derivatives. The heating temperature is, for example, 30-300°C, preferably 50-250°C, more preferably 70-200°C, and even more preferably 80-150°C.

[Example]

The present invention is further described below with reference to the following embodiments. The present invention is not limited to the following embodiments.

(Example 1)

First, a 25μm thick iodine-based polarizing film with a surface protective film was prepared. The surface of the polarizing film opposite the surface protective film was cleaned with ethanol and dried, and then subjected to a corona discharge treatment. Separately, a 0.7mm thick crystal substrate was prepared and ultrasonically cleaned in acetone for 10 minutes. After drying, the surface was subjected to a corona discharge treatment. Next, an ethanol solution containing 0.1% by weight of a triazine derivative (product name: MB1015 aqueous solution, manufactured by Iou Chemical Laboratory Co., Ltd.) was applied to the corona discharge-treated surface of the polarizing film by spin coating (applied volume: 2 ml, spin speed: 3000 rpm). The solution was then dried at room temperature, thereby forming the triazine derivative on the surface of the polarizing film. Similarly, an ethanol solution containing 0.1% by weight of a triazine derivative (product name: MB1015 aqueous solution, manufactured by Iou Chemical Laboratory Co., Ltd.) was applied to the corona discharge-treated surface of the quartz substrate by spin coating (applied volume: 2 ml, spin speed: 3000 rpm). The solution was then dried in a hot air drying oven at 80°C for 10 minutes, thereby forming the triazine derivative on the surface of the quartz substrate. Next, the polarizing film and the quartz crystal substrate, each with the triazine derivative-coated surfaces, were overlapped and heat-pressed using a hot press (pressure: 5 MPa, temperature: 120°C, time: 20 minutes) to produce a polarizing plate (surface protection film/iodine-based polarizing film/bonding layer/quartz crystal substrate).

(Example 2)

First, a 25μm thick iodine-based polarizing film with a surface protective film was prepared. The surface of the polarizing film opposite the surface protective film was cleaned with ethanol and dried, and then subjected to a corona discharge treatment. Separately, a 0.7mm thick sapphire substrate was prepared and ultrasonically cleaned in acetone for 10 minutes. After drying, the surface was subjected to a corona discharge treatment. Next, an ethanol solution containing 0.1% by weight of a triazine derivative (product name: MB1015 aqueous solution, manufactured by Iou Chemical Laboratory Co., Ltd.) was applied to the corona discharge-treated surface of the polarizing film by spin coating (applied volume: 2 ml, spin speed: 3000 rpm). The solution was then dried at room temperature to form the triazine derivative on the surface of the polarizing film. Similarly, an ethanol solution containing 0.1% by weight of a triazine derivative (product name: MB1015 aqueous solution, manufactured by Iou Chemical Laboratory Co., Ltd.) was applied to the corona discharge-treated surface of a sapphire substrate by spin coating (applied volume: 2 ml, spin speed: 3000 rpm). The solution was then dried in a hot air drying oven at 80°C for 10 minutes to form the triazine derivative on the surface of the sapphire substrate. Next, the polarizing film and sapphire substrate, each with the triazine derivative-coated surfaces, were overlapped and heat-pressed using a hot press (pressure: 5 MPa, temperature: 120°C, time: 20 minutes) to produce a polarizing plate (surface protection film/iodine-based polarizing film/bonding layer/sapphire substrate).

(Comparative example 1)

First, a 25μm thick iodine-based polarizing film with a surface protective film was prepared. The surface of the polarizing film opposite the surface protective film was cleaned with ethanol and dried, and then subjected to a corona discharge treatment. Separately, a 0.7mm thick crystal substrate was prepared and ultrasonically cleaned in acetone for 10 minutes. After drying, the surface was subjected to a corona discharge treatment. Next, an adhesive layer (thickness: 15μm, NCF-211S, manufactured by Lintec Co., Ltd.) was laminated to the corona discharge-treated surface of the polarizing film. A crystal substrate was laminated to the adhesive layer's surface opposite the polarizing film and pressed with a hand roller to produce a polarizing plate (surface protection film/iodine-based polarizing film/adhesive layer/crystal substrate).

(Comparative example 2)

First, a 25μm thick iodine-based polarizing film with a surface protective film was prepared. The surface of the polarizing film opposite the surface protective film was cleaned with ethanol and dried, and then subjected to a corona discharge treatment. Separately, a 0.7mm thick crystal substrate was prepared and ultrasonically cleaned in acetone for 10 minutes. After drying, the surface was subjected to a corona discharge treatment. Next, an acrylate-based UV-curable adhesive (LOCTITE AA3105, 100% solids, manufactured by Henkel Japan Co., Ltd.) was applied to the corona discharge-treated surface of the polarizing film using a spin coating method (applied volume: 2 ml, spin speed: 3000 rpm) to form a coating layer. The polarizing film and the quartz crystal substrate were then superimposed with the coating layer and pressed with a hand ink roller. UV rays were then applied from the quartz crystal substrate side using a UV irradiation device to achieve an accumulated radiation dose of 1000 mJ/ ^cm² on the surface, curing the UV-curable adhesive. This produced a polarizing plate (surface protection film/iodine-based polarizing film/UV-curable adhesive layer/quartz crystal substrate).

The polarizing plates obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated as follows. The evaluation results are shown in Table 1. In the following evaluations, polarizing plates with the surface protective film peeled off were used.

(Durability Assessment)

Polarizing plates (23 mm x 20 mm) obtained in the Examples and Comparative Examples were irradiated with laser light (wavelength: 455 nm) for two minutes from the polarizing film side of the polarizing plates using a laser irradiator while air was blown at a constant speed. The temperature of the highest point within the polarizing film surface was measured using a thermal imaging device from the polarizing film side, and the surface temperature of the polarizing film was determined. The appearance of the polarizing film within the polarizing plates after laser irradiation was evaluated visually and using a projected image of the polarizing plates when backlighting was used, according to the following criteria.

In addition, the polarizing plate is configured so that the polarizing film absorbs the polarized light of the laser (the polarized light of the laser is parallel to the absorption axis of the polarizing film).

○: No change in appearance or projected image

△: Slight changes in appearance (such as bumps and wrinkles) are visible, and slight changes in the projected image (such as deformation and unevenness) are visible.

×: Changes are visible in the appearance (bumps, wrinkles, etc.), and changes are visible in the projected image (deformation, unevenness).

××: Obvious changes in appearance (bumps, wrinkles, etc.) and changes in the projected image (deformation, unevenness) are seen.

As shown in Table 1, the polarizing plate of Example 1, which was fabricated by using a molecular bonding agent using molecular bonding technology to bond the polarizing film to a quartz substrate via chemical bonding, exhibited a lower surface temperature of the polarizing film after laser irradiation compared to the polarizing plates of Comparative Examples 1 and 2, and showed superior appearance and projected image quality. Furthermore, as shown in Table 1, the polarizing plate of Example 2, which was fabricated by using a molecular bonding agent using molecular bonding technology to bond the polarizing film to a sapphire substrate via chemical bonding, exhibited an even lower surface temperature of the polarizing film, and showed superior appearance and projected image quality after laser irradiation.

As described above, polarizing plates bonded using molecular bonding technology reduce the thermal load on the PVA polarizing film and ensure strong adhesion between the support substrate and the polarizing film. This prevents the PVA polarizing film from experiencing poor appearance due to thermal shrinkage, resulting in high durability that maintains the performance of the PVA polarizing film over a long period of time. Therefore, polarizing plates bonded using molecular bonding technology are particularly useful in applications that utilize light sources with large or high values of beam intensity, luminosity, brightness, and optical density.

1: Polarizing plate 2: Polarizing film 3: Bonding layer 4: Support substrate

Claims (6)

A polarizing plate is characterized by comprising: a polarizing film made of a polyvinyl alcohol-based resin; and a light-transmitting support substrate laminated on at least one side of the polarizing film via a bonding layer. The bonding layer is formed of a molecular binder that chemically links the polarizing film and the support substrate. The molecular binder contains a triazine derivative, and the triazine derivative is a compound containing two or more OH groups and/or OH-generating groups and one triazine ring. The polarizing plate of claim 1, wherein the OH groups on the surface of the supporting substrate and/or the OH groups on the surface of the polarizing film are chemically bonded to the OH groups or OH-generated groups of the triazine derivative by dehydration condensation. The polarizing plate of claim 1 or 2, wherein the thickness of the bonding layer is less than 5 μm and greater than 0.001 μm. The polarizing plate of claim 1 or 2, wherein the supporting substrate is made of one or more materials selected from organic materials, inorganic materials, and organic-inorganic hybrid materials. The polarizing plate of claim 1 or 2, wherein the thermal conductivity of the supporting substrate is greater than 1 W/mK. A method for manufacturing a polarizing plate, as claimed in any one of claims 1 to 5, characterized by comprising: a step of providing the molecular binder on the surface of the polarizing film and/or the support substrate; a step of layering the molecular binder present on the surface of the polarizing film and/or the support substrate; and a step of hot-pressing the polarizing film and the support substrate to bond the polarizing film and the support substrate by chemical bonding.